I define my own structure for the .Site.Author in config.toml and use that in my custom partials that override the internal templates.
Example in config.toml:
[Author]
name = "Foo Bar"
email = "Foo.Bar@example.com"
bio = "Foo Bar's bio."
[Author.photo]
url = "images/me.jpg"
width = 400
height = 400